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Reinforced concrete bridges located in coastal environment are known to undergo structural degradation due to chloride‐induced corrosion of reinforcement. In this paper, reliability‐based methodologies have been formulated for safety assessment of in‐service reinforced concrete T‐girders against shear and cracking limit states. The proposed methodologies incorporate the following features: (a) gain in concrete compressive strength with time, (b) the time‐dependent diffusion of chlorides into cover concrete, (c) the chloride‐induced corrosion of both stirrups and main rebar of pitting type, (d) the corrosion current variation along the span, (e) the reduction in yield strength of stirrups after it starts corroding, and (f) corrosion crack formation due to the accumulation of the corrosion products. The system reliability concept is embedded in the framework of Monte Carlo simulation, for estimating the time‐variant failure probabilities. The usefulness of the methodology is demonstrated on a typical in‐service Chennai flyover, designed according to MORTH. The girder fails to meet the target reliability index consideration in the case of shear limit state and also fails the required serviceability criteria even before the end of 50 years. This example brings out the need to consider time‐variant reliability considerations at the design stage itself.

As the infrastructure age, their assessment to carry the loads they are subjected to becomes increasingly important. Also, assessment is needed as part of a regular monitoring programme. Before carrying out a rigorous probabilistic analysis for assessment, it is often required to make a preliminary assessment using simplified procedures, such as that developed using semi-probabilistic approach, in which partial factors are used. In this article an attempt has been made to evolve a framework to determine the partial factors for safety assessment of the in-service T-girder bridges in India against the limit state of shear. Limit state of shear is considered because it is one of the important ultimate limit states for bridge girder that results in brittle failure. The partial factors are derived using first order reliability method. In order to suggest a simple method for safety assessment, statistical properties of modelling error associated with the simplified equation of shear capacity estimation are estimated using test data of 185 beams reported in the literature. To demonstrate the usefulness of the framework developed, an attempt has been made to determine partial factors for assessment for a typical T-girder bridge designed according to the relevant Indian codes. The loading considered corresponds to actual traffic loads on a typical Chennai flyover. The study reported here gains importance as: (i) general guidelines to assess the reliability of in-service bridges are non-existent in the Indian context and (ii) the partial factors suggested for two consequence classes can be used for quick assessment of the safety of existing similar flyover girders against limit state of shear in a more rational way.Keywords: Assessment, RC T girder bridges, partial factors, reliability index. THE safety assessment of bridges plays a key role in a country's economic development. Its increasing importance is felt in most countries. As the processes involved in assessments are complex and time-consuming, various levels of assessment are done; each of the higher level is less conservative and involves more work in terms of computation 1 . When a particular assessment level is found satisfactory, then proceeding through further levels of assessments is not required. The complexity in assessment is thus minimized. Generally, the initial (or preliminary) assessment level is done in a deterministic way using partial factors, evaluated using a probabilistic analysis. Generally, in literature, such methods are referred to as semi-probabilistic methods 2 . Partial factors are commonly used in designing structures. In the assessment, these values are used to determine target resistance values, against which the resistance of an in-service bridge needs to be checked. It is important to note that partial factors to be used in assessment are not the same as the design, because of differences in target reliability indices that are considered 3 . The target reliability levels required for in-service bridges are lower than those of new bri...

Using the concept of information theoretic entropy, the probability density function (pdf) of shear capacity of the reinforced concrete beam with stirrup reinforcement is determined. Entropy, expressed in terms of Shannon functional, is maximized subjected to the statistical moment and normalization constraints of pdf of shear capacity. The statistical moments of shear capacity distribution are obtained using second-order approximation of shear capacity equation. The pdf so determined has strong statistical mechanics interpretation of maximum entropy principle. Also, a procedure for goodness-of-fit test has been proposed, for the given data, using the information theoretic entropy as a measure of goodness-of-fit. In the present investigation, beams of three different ranges of shear span to effective depth ratios are considered. The mechanics-based shear capacity equations, presented earlier by authors along with associated modelling errors, are used for estimating the statistical moments of shear capacity distribution. The computationally efficient approach of determination of maximum entropy distribution presented in this article can be viewed as an alternate to the process of determination of pdf using brute force Monte Carlo simulation approach.